The present invention relates to a two-dimensional image detector such as an X-ray sensor and an image sensor, that is used in an X-ray pickup device or an X-ray diagnostic image display device for forming an X-ray image passing through a human body and that is capable of detecting an image of radiation such as an X-ray, visible light, and infrared light, and the present invention further concerns an active-matrix substrate used for the detector and a pixel defect correcting method of the two-dimensional image detector.
Conventionally, as a flat-panel image sensor for radiation that serves as a two-dimensional image detector, the following construction has been known: semiconductor sensors are two-dimensionally arranged in a row direction and a column direction, a switching element is provided for each pixel electrode, and the switching elements are successively turned on for each column so as to read electrical charge for each column. The semiconductor sensor is formed by stacking a semiconductor layer with photoconductivity and a pixel electrode, and the semiconductor sensor detects an X-ray and generates electrical charge (electron-hole pair).
The construction and principle of such a flat-panel image sensor are described in xe2x80x9cD. L. Lee, et al., xe2x80x98A New Digital Detector for Projection Radiographyxe2x80x99, SPIE, 2432, pp. 237-249, 1995xe2x80x9d (published in 1995), xe2x80x9cL. S. Jeromin, et al., xe2x80x98Application of a-Si Active-Matrix Technology in a X-ray Detector Panelxe2x80x99, SID 97 DIGEST, pp. 91-94, 1997xe2x80x9d (published in 1997), and Japanese Laid-Open Patent Publication No.342098/1994 (Tokukaihei 6-342098, published on Dec. 13, 1994).
The following briefly describes the construction and principle of the conventional flat-panel image sensor.
Firstly, as an active-matrix substrate used for the flat-panel image sensor, it is possible to adopt an active-matrix substrate used in a liquid crystal display device and so on.
Namely, as shown in FIGS. 18 and 19, an active-matrix substrate 101 is provided with electrode wires having gate electrodes 102 and data electrodes 103 arranged in a lattice form. Each intersection includes a thin-film transistor (xe2x80x9cTFT: Thin Film Transistorxe2x80x9d) 104 acting as a switching element, a pixel electrode 110 connected via the TFT 104 to the data electrode 103, and a storage capacitor (Cs) 106 connected in series with the pixel electrode 110.
A photoconductive film 107 for directly converting light, an X-ray, etc. to electrical charge is formed on an upper layer of the active-matrix substrate 101 so as to complete a two-dimensional image detector such as an X-ray sensor and a flat-panel image sensor 100.
In other words, electrical charge generated by the photoconductive film 107 is accumulated in the storage capacitor (Cs) 106 by a high voltage, data is stored as electrical charge of each pixel according to the pattern of a subject. The data is successively scanned by the gate electrodes 102 acting as scanning lines, a circuit such as an operation amplifier for reading pixel data as a signal, which is selected by the scanning line, takes out an object projected on a sensor as an image data.
Incidentally, on the active-matrix substrate 101, in the event of a defect on the TFTs 104 or a property defect on the photoconductive film 107, etc. in a pixel, the pixel is recognized as a pixel defect (point defect).
Additionally, in the case of an off-property defect of the TFTs 104, i.e., a resistant value not sufficiently increased when the operation is turned off, a leakage defect on the photoconductive film 107, or a defect of extraordinally high sensitivity on the photoconductive film 107, even when the gate electrodes 102 are in a non-selection period, unnecessary electrical charge keeps leaking from the pixel to the data electrodes 103. Thus, the data electrodes 103 connected to the pixel are recognized as a line defect.
Generally, when a pickup image is displayed based on image data captured by the flat-panel image sensor 100, a line defect is more noticeable than a pixel defect (point defect), and it is difficult to correct the defect by image data processing.
Therefore, in the event of a pixel defect causing the above line defect, it is desirable to make correction on the pixel.
However, the conventional active-matrix substrate, the conventional two-dimensional image detector having the same, and the conventional method of correcting a pixel defect in the two-dimensional image detector do not refer to a method of correcting such a pixel defect.
The main objective of the present invention is to provide an active-matrix substrate which can readily suppress leakage of unnecessary electrical charge from a pixel defect, which may cause a line defect.
In order to attain the above objective, the active-matrix substrate of the present invention includes a pixel defect correcting part on a part of an electrode for connecting data electrodes and a pixel electrode, which is connected to the data electrodes via switching elements disposed respectively at intersections of gate electrodes and the data electrodes arranged in a lattice form.
Namely, the active-matrix substrate is provided with electrode wires having the gate electrodes such as scanning lines and the data electrodes such as signal lines arranged in a lattice form, the switching elements such as thin-film transistors (TFT) disposed respectively at intersections of the lattice form, the pixel electrode connected to the data electrodes via the switching elements, and storage capacitors connected to the pixel electrode.
Therefore, when the active-matrix substrate is used as a display device, the gate electrode is selected as the corresponding scanning line and a gate voltage is applied to the switching element such as the thin-film transistor (TFT) connected to the corresponding pixel electrode, so that an information signal is applied to the pixel electrode from the data electrode such as a signal line, and electrical charge is accumulated in the storage capacitor so as to display the pixel.
Meanwhile, in the case of the active-matrix substrate used as the flat-panel image sensor, when radiation such as an X-ray is emitted from the outside to the corresponding pixel, electrical charge is accumulated in the storage capacitor via the photoconductive film. Hence, the gate electrode is selected as the corresponding scanning line and a gate voltage is applied to the switching element such as the thin-film transistor connected to the pixel electrode of the corresponding pixel, so that an information signal based on electrical charge accumulated in the storage capacitor is applied to the data electrode such as a signal line via the pixel electrode, and the information signal is outputted to the outside.
In the present invention, a pixel defect correcting part is provided on a part of the electrode connecting the data electrode and the pixel electrode. Here, the xe2x80x9cpixel defect correcting partxe2x80x9d refers to a part which is cut by laser to correct a pixel defect.
Hence, the pixel defect correcting part is subjected to spot radiation of laser from the back of the active-matrix substrate so as to readily cut the pixel defect correcting part.
With this arrangement, for example, in a two-dimensional image detector, etc. including the photoconductive layer on the active-matrix substrate, it is possible to prevent unnecessary electrical charge caused by a pixel defect from leaking to the data electrode through the switching element.
Consequently, a defect recognized as a line defect before correction is corrected to a pixel defect (point defect) on a single pixel, so that the defect becomes more unnoticeable. Furthermore, a defect can be readily corrected by image data processing.
Thus, it is possible to provide the active-matrix substrate which can readily suppress leakage of unnecessary electrical charge from a pixel defect, which may cause a line defect.
For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.